Gravity and magnetic anomalies interpretation from satellite data, at the Guayana shield

Bolivar and Amazonas states, Venezuela

Abstract

The results of the integration of satellite gravimetric and magnetic data are presented, and in geological terms, those of the Guiana Shield as part of the homonymous craton in Venezuelan territory, Bolívar and Amazonas states. Maps of relief, Free Air Anomalies (FAA), Bouguer Anomalies (BA), and Magnetic Anomalies (MA) were created from the satellite databases ETOPO1, EIGEN 6C4, and EMAG2 v3, mapped using the GMT (Generic Mapping Tools) software. The procedure of upward analytical continuation (UAC) of the field was applied, and the UAC 80km was selected as the most appropriate for the regional-residual separation, since it does not experience major variations, even if that height is increased. Both the BA map and the regional BA map (UAC 80km) illustrate the regional effect of the Shield, with the oblong shape of the contours that outline the Shield's morphology. This regional trend is also well expressed on a large scale by the regional UAC 35km and 50km contours of the magnetic anomaly data.

The final and most important product of this study is the map of the depth of the Moho discontinuity in the Guiana Shield, which should be highlighted as the first of its kind for the Venezuelan Guiana area and has been generated by the inversion of satellite gravimetric data. The deepening of the Moho from west to east is observed in a range of 41 to 44.5 km, with the maximum depth to that interface reached between 59°- 63° W longitude and 4°- 6° N latitude. The BA contours associated with the Moho show the gravimetric response of an oblong structure with a preferential E-W orientation and gentle gradients on its flanks, mainly to the south and west. Towards the northeast, an increase in the gradient is noted, and the E-W orientation is maintained over terrains of the Imataca Province. The Moho contours in the south-central region of Amazonas State are oriented in a NW direction, aligned with the series of paleorifts that characterize that region of the Shield; and the regionals, both gravimetric and magnetic, show the contact between the Casiquiare and Ventuari domains. The gravimetric regional reflects the dip of the Moho towards the NE, which is the largest component of this regional.